Die-cast piston



March 30, 1948 F. J. srucKER'r DIE CAST PISTON Filed Sept. 24, 1945 @www Patented Mar. 3.0, 1948 UNITED STATES PATENT OFFICEy DIE-CAST Pxs'roN Felix J Stuckert, Wauwatosa, Wis., 'assigner to Y Briggs & Stratton Corporation, Milwaukee, Wis., a corporation of Delaware Application September 24, 1945, Serial No. 618,189

(ci. aos-1o) l 4 Claims. 1

This invention relates to pistons for internal combustion engines and has particular reference to die cast pistons.

As is well known, a piston for an internal combustion engine comprises a head, a cylindrical skirt extending from one side of the head, and wrist pin bearing bosses projecting radially inwardly from the interior of the skirt intermediately of its ends.

It is usual practice to reinforce die cast pistons by connecting the wrist pin bosses with the piston head and this is accomplished in most instances by casting ribs on the inner Wall of the piston having at least the same width or diameter as the wrist pin bosses.

While this expedient provides the necessary reinforcement, it has been found objectionable inasmuch as it tends to make the piston excessively heavy by reason of the large body of metal between the pin bosses and the piston head, a condition which also is responsible for improper cooling of the casting and warping. Further, it has been found that because of the mass of the reinforcing ribs, the die casting is apt to be spongy to varying degrees making it extremeli difficult to produce a balanced piston.

With these objections in mind, it is one of the purposes of this invention to provide an improved construction for die cast pistons wherein the inner wall of the piston has reinforcing ribs thereon joining the wrist pin bosses with the piston head but with the ribs of minimum thickness, consistent with strength, and considerably less than the diameter of the pin bosses but so constructed and arranged as to enable die casting the piston.

More specifically it is an object of thisrinvention to provide an improved piston construction wherein the wrist pin bosses are reinforced by ribs joined to the side wall of the piston and connecting the bosses with the piston head, with the ribs having a substantial-ly angle shaped cross section.

It is another object of this invention to provide an improved piston reinforced by angle shaped ribs of the character described wherein one leg of each rib projects substantially radially inwardly from the cylindrical skirt of the piston in tangential relationship to its boss with said legs parallel to but lying at opposite sides of a plane containing the axes of the piston and wrist pin bosses and wherein the other 'leg of each rib extends across the inner end of the wrist pin boss to transmit force from the piston head directly 2 and squarely onto the inner end portion of the boss.

With the above and other objects in view, which will appear as the description proceeds, this lnvention resides in the novel construction, combination, and arrangement of parts substantially as hereinafter described, and more particularly dened by the appended claims, it being understood that such changes in the precise embodiment of the hereindisclosed invention may be made as come within the scope of the claims.

The accompanying drawing illustrates one complete example of the physical embodiment of the invention constructed in accordance with the best mode so far devised for the practical application of the principles thereof, and in which:

Figure l is a side elevational view of the piston of this invention with parts thereof broken away and in section to better illustrate the reinforcing rib for the pin boss;

Figure 2 is an end view of the piston shown in Figure 1 looking into the open end thereof and having one of the wrist pin bosses broken away to illustrate the substantially angle shaped reinforcing rib connecting the boss with the piston head; and

Figure 3 is a longitudinal sectional view taken through Figure 2 on the plane of the line 3-3.

Referring now more particularly to the accompanying drawing in which like numerals indicate like parts, the numeral 5 generally designates the piston of this invention. The piston comprises the usual substantially cylindrical skirt 6 closed at one end by a wall l normal to the skirt axis and providing the head of the piston.

The inner wall or the skirt has diametrically opposite wrist pin bosses 8 cast thereon and aligning on an axis intersecting the skirt axis but nornected in the usual manner to the connecting rod of an engine.

in order to accomplish the purposes of this invention ribs l@ are cast on the piston to reinforce the wrist pin bosses. These ribs are located on the inner wall of the skirt and extend longitudinally between the bosses and the piston head to firmly join these parts together.

As is clearly illustrated in Figures 1 and 2, the ribs i@ are substantially angle shaped in cross section with one leg il of each rib projecting substantially radially from the cylindrical wall of the skirt tangentially of its boss with the legs I l parallel to but lying at opposite sides of a plane containing both the axes of the wrist pin bosses and that of the piston itself.

The other llegs I2 of the angle shaped ribs are substantially concentric to the cylindrical skirt of the piston and join the projecting inner ends of the bosses remote from the skirt with the piston head, to reinforce the bosses against the thrust imposed thereon during use of the piston. It follows, therefore, that the legs I2 of the ribs overlie the cylindrical skirt and face each other at the central area of the piston, and attention is directed to the fact that these inner faces of the -legs I2 are arcuate and concentric to the piston axis and flush with the correspondingly curved inner ends of the wrist pin bosses.

The legs II and I2 of the ribs cooperate with the sides of the piston to define channels the bottoms oi' which are provided by the legs I I, the sides of the channels at opposite end portions of the bosses being provided jointly by the legs vI2 and the wall of the skirt which they overlie.

Inasmuch as the legs II of the ribs lie at opposite sides ofa plane containing both the axes of the wrist pin bosses and the piston itself, it obviously follows that the channels open to the interior of the piston at opposite sides of this same plane. Because of this fact it is possible to die cast the piston f this invention even though the space above the wrist pin bosses, i. e. between the wrist pin bosses and the head of the piston, is largely cored out.

In die casting the piston a two-part mold is used, one part being designed to p'ull straight out of the cast piston and away fromthe other part, which by virtue of the defined shape and construction of the ribs, then may be rotated clear of the wrist pin bosses for withdrawal from the piston.

Attention is directed to the fact that the Wall thickness of the legs II and I2 is substantially no greater than that of the wall thickness of the bosses. This assures maximum strength without excessive piston weight.

From Figure 1 it will also be noted that the bosses have a substantially D shape as viewed along the Wrist pin axis with the piston axis vertical and that the legs I I of the angle shaped ribs are disposed in line with the vflat sides I3 of the bosses.

As stated, the particular shape and proportion of the ribs I0 assures adequate reinforcement of the piston and especially the wrist pin bosses with a minimum amount of metal. This is highly advantageous because of the fact that heavy die cast sections of metal are apt to be spongy and should be avoided as they make balancing of the piston an extremely diiiicult task and also lead to warping:

Moreover, considerable saving in metal and cost is eifected by providing the piston of this invention With substantially angle shaped reinforcing ribs projecting from the wall of the piston and joining the internally projecting ends of the bosses with the piston head.

From the foregoing description taken in connection with the accompanying drawing, it will be readi-ly apparent to those skilled in the art that the piston of this invention is especially well 'suited for production by die casting methods by reason of the particular shape of the ribs which reinforce the wrist pin bosses on the inner wall of the piston skirt.

What I claim as my invention is:

1. A cast piston of the character described, comprising: a. head; a substantially cylindrical skirt extending from one side of the head; diametrically opposite axially aligned wrist pin bosses projecting inwardly from the skirt; reinforcing ribs cast on the inside of the skirt and joining the pin bosses with the piston head, said ribs being substantially angle-shaped in cross section with one leg of each rib projecting inwardly from the skirt in tangential relationship to its boss with said legs parallel to but lying vat opposite sides of a plane containing the pin and piston axes, the adjacent inner extremities of the pin bosses being curved concentric to the skirt, and the other legs of said ribs extendingacross the inner end portions of the pin bosses and likewise being curved in'concentric relationship to the skirt, said other legs holding the inner extremities of the bosses in axial alignment against the thrust imposed thereon during use of the piston; and surfaces on the sides of said bosses opposite the piston head substantially normal to and connecting with the inner sides of said first designated legs.

' the pin bosses with the piston head, said ribs being substantially angle-shaped in cross section with one leg of each rib projecting inwardly from the skirt tangentlally to its boss with said legs parallel to but lying at opposite sides of a plane containing the pin and piston axes, the other legs of the ribs extending across the inner end portions of the pin bosses and facing each other adjacent to the central portion of the piston to hold said inner end portions of the bosses in axial alignment against the thrust imposed thereon during use of the piston, said other legs an-d the surfaces of the pin bosses which face each other being concentric tothe cylindrical skirt of the piston, and said legs of the reinforcing ribs having a thickness substantially no greater than that of the pin boss walls so as to hold the weight of the piston to a minimum.

3. In a c ast piston of the character described: a head; a substantially cylindrical skirt extending from one side of thehead; diametrically opposite axially aligned wrist pin bosses projecting inwardly fromr the skirt with their inner adjacent ends vterminating in arcuate surfaces concentric With the piston skirt; reinforcing means extending longitudinally along'the wall of the skirt and joining the bosses with the piston head, said reinforcing means cooperating with the wall of the-skirt to provide a substantially channelshaped rib construction by which the pin b-osses are reinforced against thrust imposed thereon during use of the piston, the backs of the channels being parallel to the axis of the piston and projecting eccentrically from the wall of the skirt at opposite sides of a plane containing the piston and pin axes and tangentially to their respective bosses so that the channels open to opposite sides of said plane containing the piston and pin axes, and the walls of the channels facing the inner surface of the skirt being concentric with the skirt. i

4. A cast piston of the character described comprising: a head; "a substantially cylindrical skirt depending from the head; diametrically opposite axially aligned wrist pin bosses projecting inwardly from the inner Wall surface of the skirt; reinforcing means on said bosses including an arcuate wall substantially concentric to the cylindrical skirt Joining the inner end portion ot each Din boss with the piston head to reinforce the bosses against thrust imposed thereon during use of the piston; and an eccentrlcally-disposed 1ongitudinal rib projecting inwardly from the inner wall surface of the skirt and tangent to one side of eachof the bosses. said ribs lying at opposite sides of a plane containing the piston and pin axes and being parallel to one another. the top and bottom sides of the bosses adjacent to their junctions with said ribs having relatively nat surfaces substantially parallel to one` another and joining the ribs substantially in perpendicular relationship thereto.

FELIX J. STUCKERT.

BWEBENCES CITED The following references `are of record in the me of this patent: 

